title: Interplay between structure and dynamics in chitosan films investigated with solid-state NMR, dynamic mechanical analysis, and X-ray diffraction.
abstract: Modern solid-state NMR techniques, combined with X-ray diffraction, revealed the molecular origin of the difference in mechanical properties of self-associated chitosan films. Films cast from acidic aqueous solutions were compared before and after neutralization, and the role of the counterion (acetate vs Cl(-)) was investigated. There is a competition between local structure and long-range order. Hydrogen bonding gives good mechanical strength to neutralized films, which lack long-range organization. The long-range structure is better defined in films cast from acidic solutions in which strong electrostatic interactions cause rotational distortion around the chitosan chains. Plasticization by acetate counterions enhances long-range molecular organization and film flexibility. In contrast, Cl(-) counterions act as a defect and impair the long-range organization by immobilizing hydration water. Molecular motion and proton exchange are restricted, resulting in brittle films despite the high moisture content.
authors.affiliation: Calle 62 No 52-59 Lab 310, University of Antioquia, Sede de Investigaciones Universitarias, SIU, Medellín, Colombia.
authors.forename: Carmiña
authors.initials: C
authors.lastname: Gartner
authors.forename: Betty Lucy
authors.initials: BL
authors.lastname: López
authors.forename: Ligia
authors.initials: L
authors.lastname: Sierra
authors.forename: Robert
authors.initials: R
authors.lastname: Graf
authors.forename: Hans W
authors.initials: HW
authors.lastname: Spiess
authors.forename: Marianne
authors.initials: M
authors.lastname: Gaborieau
mesh_terms: D048271:Chitosan / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D014961:X-Ray Diffraction / Q000379:methods*
chemical_list: D048271:Chitosan